Field of the Invention
The present invention relates to an ultrasound signal processor, an ultrasound signal processing method, and an ultrasound diagnostic device including the processor and the method, and in particular relates to a reception beam forming processing method in an ultrasound signal processor using a color flow mapping method, and color flow mapping calculation processing.
Description of the Related Art
An ultrasound diagnostic device transmits ultrasound to the inside of a subject with an ultrasound probe (hereinafter referred to as a “probe”), and receives reflected ultrasound (echo) caused by difference in acoustic impedance of subject tissue. Further, the ultrasound diagnostic device generates an image indicating a structure of internal tissue of the subject on the basis of an electric signal obtained from the received ultrasound, and displays the image on a monitor (hereinafter referred to as a “display”). The ultrasound diagnostic device has been widely used for morphological diagnosis of a living body since it is less invasive to the subject and a state of body tissue can be observed in real time with a tomographic image and the like.
In recent years, many ultrasound diagnostic devices are equipped with a color flow mapping (CFM) method. In the CFM method, a Doppler shift (frequency shift) is detected occurring in the echo caused by movement of body tissue such as a bloodstream, and velocity information as a two-dimensional image is superimposed and displayed on a two-dimensional tomographic image (B mode tomographic image). In order to detect the Doppler shift, it is necessary to transmit and receive the ultrasound repeatedly at the same position within the subject. Hereinafter, the number of times of transmitting and receiving the ultrasound to the same position is referred to as an “ensemble number,” and an image generated with the CFM method is described as a “color Doppler image.”
In the color Doppler image, image quality is improved as the ensemble number is increased; however, a problem has been known in which a frame rate is decreased since the number of times is increased of transmission and reception of ultrasound required. For that reason, a technique has been studied for improving quality of the color Doppler image regardless of the ensemble number, such as the technique disclosed in JP 2011-500261 A and JP 2005-177338 A, for example. In addition, a technique has been studied for improving the frame rate by not repeatedly performing transmission and reception of ultrasound to the same area by the ensemble number, such as the technique disclosed in JP 2002-224107 A, for example.
However, it is difficult to apply the techniques described in JP 2011-500261 A and JP 2005-177338 A when trying to improve the image quality by increasing the ensemble number. In addition, in the technique described in JP 2002-224107 A, there is a problem that it is not possible to keep the quality of the color Doppler image when trying to achieve further improvement of the frame rate.